Device for measuring the friability of particulate solid materials

ABSTRACT

A method and a device for measuring the friability of particulate solid materials. The device comprises a chamber, having an inlet for gas and an outlet for fractured particles of the solid material in operative connection with means for its vibration. The chamber has a screen horizontally mounted and means for measuring the amount of material which is fractured and passes through the screen when the container is vibrated. In operation, gas is injected through the inlet to force the fractured material through the outlet.

United States Patent [1 1 3,636,772 Bennett 51 Jan. 25, 1972 [s41 DEVICEFOR MEASURING THE FOREIGN PATENTS OR APPLICATIONS [72] Inventor: HaroldL. Bennett, Sanford, Mich.

[73] Assignee: The Dow Chemical Company, Midland,

Mich

[22] Filed: Feb. 24, 1970 [2]] App]. No.: 13,715

52 US. Cl. ..73/432 11,73/7/ [51] v ..G0ln 19/00 [58] Field of Search..73/432 R; 241/84, 94, 175; 209/321 [56] References Cited UNITED STATESPATENTS 3,511,078 5/1970 Rajkai ..73/432 R FRIABILITY OF PARTICULATESOLID MATERIALS 1,283,676 12/1961 France ..241/175 Primary ExaminerS.Clement Swisher Attorney-Griswold & Burdick, Jerome L. Jeffers andWilliam R. Norris [5 7] ABSTRACT A method and a device for measuring thefriability of particulate solid materials. The device comprises achamber, having an inlet for gas and an outlet for fractured particlesof the solid material in operative connection with means for itsvibration. The chamber has a screen horizontally mounted and means formeasuring the amount of material which is fractured and passes throughthe screen when the container is vibrated. In operation, gas is injectedthrough the inlet to force the fractured material through the outlet.

4 Claims, 1 Draw'ng Figure Source of vibraono/ eneryy Par/ic/es Meas Ar/n9 ev/ce DEVICE FOR MEASURING THE FRIABILITY OF PARTICULATE SOLIDMATERIALS BACKGROUND OF THE INVENTION Certain friable materials such ascaustic soda, calcium chloride, sodium chloride and other semirigidsolids are produced in the form of particulate granules or flakes. Thisfacilitates their use as dry chemicals in formulations as well as forlarge scale operations such as melting ice on roadways.

A problem arises in the marketing of these products due to theirpropinquity to break up into small fragments producing a dusty material.Methods are available for producing less friable particles and thusavoiding the dusting problem. However, in order to insure adequatequality control, a convenient means of testing the friability of theparticles is needed.

Methods are known for measuring the strength of solid materials such ascoke. One such method is the ASTM Drop Shatter Test for Coke,Designation Dl4l-48, wherein the coke is shattered and a relativestrength index, usually reported as the weight percent of the originalcoke passing through or being caught in a sieve of some arbitrary size,is determined. Such a testing method is not readily adaptable fortesting particles which shatter into dust due to the difficulty incollecting sufficient dust particles for quantitative measurement.

It would be desirable, and it is the object of the present invention toprovide a novel device for measuring the friability of particulate solidmaterial.

An additional object is to provide such a device which willquantitatively measure the friability of materials which break up intodustlike particles.

A further object is to provide a method for quantitatively measuring thefriability of particulate solid materials which break up into dustlikeparticles.

SUMMARY OF THE INVENTION The present invention provides a device and amethod for measuring the friability of particulate solid material. Thedevice comprises a screen positioned within a vibratable chamber. Thechamber, which is substantially airtight to prevent the loss of dustparticles, is provided with an inlet for gas and an outlet for particlesof the solid material being tested. The screen has apertures smaller insize than the solid particles to be tested and is preferably mounted inthe chamber in a substantially horizontal position. A tilt of less thanabout 10 is desirable with tilt being optimal. The device is equippedwith means for measuring the amount of particulate material which pasesthrough the screen and out of the outlet upon vibrating the containerand injecting gas through the inlet. Preferably, the lower part of thechamber is funnel shaped to expedite passage of the particles to theoutlet.

DETAILED DESCRlPTlON OF THE INVENTION One embodiment of the invention isillustrated by the accompanying drawing. A chamber 12 for the testproduct is connected to a source of vibrational energy 13 in a mannerwhich permits the chamber to vibrate. A screen 14 having aperturessmaller in size than the particles to be tested is horizontally mountedin the chamber. The chamber is pre vided with an inlet for gas 15 and anoutlet for particles 16 located below the screen. In operation, the testproduct is placed on the screen and the chamber is vibrated. Thoseparticles which break into pieces small enough to pass through thescreen are blown by the gas stream out the outlet to a device 17 formeasuring their amount.

Optionally, objects 18 which are harder and heavier than the testproduct are placed upon the screen with the test product. When thecontainer is vibrated, fracturing of the test product is facilitated byaction of the heavy objects. An optional second screen 19 having smalleropenings than the first can be placed below it. The second screen willprevent any particles which are forced through the first by the weightof the heavy objects from passing through the outlet and being measuredby the measuring means.

The testing device is especially effective for testing the friability ofhygroscopic compositions such as NaOH or CaCl,. By sealing the chamberto prevent the entrance of moisture from the atmosphere and injecting asubstantially anhydrous gas through the inlet, the hygroscopic materialcan be prevented from gathering moisture during the testing. In thismanner, the friability of the dry material can be determined. Particlesin flake form are the preferred test product when high reproducibilityis desired since a granular material may partially clog the screen.

The invention is further illustrated by the following example:

Example I A device of the design set out in the drawing was set up andoperated in the following manner:

Two hundred grams of caustic flake were placed on a U.S. No. 35 screen.Twenty alumina cylinders, 34-inch diameter by 13/ l6inches, were placedon the screen with the caustic. A U.S. No. 40 screen was placed beneaththe No. 35 screen and both placed in a test chamber. The test chamberwas sealed except for the presence of 2%inch copper tubes projectingthrough its side. One piece of tubing functioned as an inlet fornitrogen gas at a rate of 0.5-1 .0 standard cubic feet per minute, whilethe other served as an outlet for fractured particles. Substantiallyanhydrous, i.e., less than 0.01 percent H O by weight, nitrogen wasemployed. By keeping the test container essentially free of moisture,plugging of the screen and changes in the friability of the test sampledue to moisture build up in the caustic were minimized.

The test chamber setup was mounted in a commercially available devicefor generating vibrational energy. As dust was generated by thevibrations, it was conveyed by the gas stream to a dust monitorconsisting of a water stream in which the caustic dust dissolved to forman electrically conducting solution. The conductivity of this solution,which was proportional to the amount of caustic passing through thescreen, was monitored continuously throughout the experiment.

After 1 minute of vibration, the caustic had a breakage rate of 0. l 5g./min. As vibration continued, the weaker flakes were depleted and thebreakage rate decreased. After 10 minutes, the rate had gone down to 0.1g./min. A plot was made of conductivity-vs.-time and integrated to get atotal breakage value (1.045 g.) for the sample. Dividing this number byduration of the experiment in minutes gave an average breakage rate of0.1 16 g./min.

By reproducing the run with a standard caustic flake of suitablestrength, the relative strength of the test sample is found by solvingthe equation:

R ST E where: M

S relative strength R, rate for standard (10 min. value) R, rate fortest sample (10 min. value) A value for S, of l or greater indicatesthat the test sample is as strong as or stronger than the standard.

The conductivity test used for measuring the amount of fractured causticin example 1 is only one of avariety of possible methods. For example, adevice for measuring the weight of material passing through the screencould be used. A particle counter could be used when the size ofparticles passing through the sieve is large enough to make countingthem practical.

We claim:

1. A method for testing the'friability of particulate hygroscopicmaterial which comprises:

3 4 a. placing the material upon a screen having apertures the outletinagiven period of time.

smaller than the particle size of the material while main- 2. Theprocess of claim 1 wherein the gas is substantially antaining the screenin a substantially air tight chamber hy r equipped with an inlet for gasand an outlet for particles; 3. The process of claim 1 wherein thematerial is NaOH or b. vibrating the screen while injecting asubstantially an- 5 zhydrous gas through the inlet to move particleswhich 4. The process of claim 1 wherein the chamber IS hermetipassthrough the screen out the outlet; and Cally saaledc. measuring theamount of material which passes through

1. A method for testing the friability of particulate hygroscopicmaterial which comprises: a. placing the material upon a screen havingapertures smaller than the particle size of the material whilemaintaining the screen in a substantially air tight chamber equippedwith an inlet for gas and an outlet for particles; b. vibrating thescreen while injecting a substantially anhydrous gas through the inletto move particles which pass through the screen out the outlet; and c.measuring the amount of material which passes through the outlet in agiven period of time.
 2. The process of claim 1 wherein the gas issubstantially anhydrous.
 3. The process of claim 1 wherein the materialis NaOH or CaCl2.
 4. The process of claim 1 wherein the chamber ishermetically sealed.